Code Cycle: 2016 & 2019 Standards
Reference: CalCERTS New Construction Training Manual Chapter 5, Section 5
Typical hot water distribution designs are often much longer than they need to be. Often the house design process does not consider the location of the water heater and distribution system relative to end use points. A compact distribution system design means that all the end use points in a non-recirculating distribution system are within a specified length of piping to the water heater that serves those fixtures. Maximum pipe run lengths that meet the compact design criteria are based on floor area served.
A compliance credit is available for installations that meet the criteria of a compact distribution system when field verified by a HERS Rater per the protocol of RA3.6.5. This is available for single family homes and multifamily dwelling served by individual water heaters. The compact distribution system verification protocol, RA3.6.5, also requires HERS verification of Pipe Insulation per RA3.6.2, See article titled "2016 & 2019 HERS Residential Hot Water Distribution Pipe Insulation Requirements."
Eligible compact hot water distribution designs can generate a compliance credit using the performance approach. There are two versions of the Compact Design credit:
- The “Basic Credit” - No HERS verification required.
- The “Expanded Credit” - HERS verification required.
Plan calculations must be completed that demonstrate that the water heater to fixture proximity is more compact than a threshold criteria that is defined based on the dwelling unit conditioned floor area and number of stories. Compactness is characterized by calculating the “Weighted Distance” from the water heater to key fixtures and the threshold criteria is identified by the “Qualification Distance”.
Weighted Distance: Calculated by the designer and verified by the HERS Rater, the weighted distance is calculated using a plan view, straight-line measurement of the distance from the water heater to the center of the furthest use point fixture in three locations: 1) the master bath, 2) kitchen, and 3) the third furthest hot water fixture. In some multifamily situations, there may not be a third furthest fixture point beyond the master bath and kitchen, resulting in the third term being ignored.
- The weighted distance varies depending on whether it is a non-recirculating or a recirculating distribution system.
- The recirculation option is only available for single family homes (RA4.4.6).
- Calculations are only based on horizontal plan view distance from the center of the water heater to the center of the fixture use point.
- Vertical pipe run lengths, such as from 1st floor to 2nd floor, are ignored.
- If multiple water heaters, the calculation is performed for each water heater using the average of the third furthest fixtures for each water heater.
Weighted Distance = LFt to MBath + LFt to Kitchen + LFt to 3rd Furthest
Qualification Distance: This is calculated by the modeling software, dependent on floor area, number of stories in the dwelling unit, number of water heaters, and if the DHW system is recirculating (available to single family only) or non-recirculating.
HERS Verification: RA3.6.5 CHWDS-H-EX
“Basic Credit” -- does not require any further verification steps to secure the compliance credit.
“Expanded Credit” -- If the builder chooses to pursue an “Expanded Credit,” additional energy savings will be recognized under the performance method and require HERS-verified.
The requirements in RA4.4.6 above (weighted distance calculations) must be met. In addition, the following HERS field verification's must be met as per RA3.6.5:
- No hot water piping > 1” diameter is allowed.
- 1” diameter piping is limited to 8 ft. or less in length.
- Two- and three-story buildings cannot have hot water distribution piping in the attic, unless the water heater is also located in the attic.
- Eligible recirculating systems must be HERS-Verified Demand Recirculation Manual Control visual inspection conforming to RA4.4.17 and RA4.4.7: